The conventional methods for producing dichlorophenylthioglycolic acid are as follows:
(1) The method in which trichlorobenzene and sodium hydrosulfide are reacted at 125.degree. C. under increased pressure in liquid ammonia solvent in the presence of copper acetate catalyst for 10 hours to yield dichlorothiophenol, which is then reacted with sodium monochloroacetate to yield dichlorophenylthioglycolic acid with a yield of 14 to 29% [Kogyo Kagaku Zasshi, 70, 1384 (1967)].
(2) The method in which dichlorobenzene is sulfonylchlorinated with chlorosulfuric acid and then reduced with a large amount of zinc powder under acidic conditions to yield dichlorothiophenol, which is then reacted with monochloroacetic acid to yield dichlorophenylthioglycolic acid with a yield of 81% (U.S. Pat. No. 3,440,288).
However, these known methods respectively have the following drawbacks.
In the method of (1) above, the use of liquid ammonia, which is difficult to handle, a difficult-to-dispose copper compound and an increased reaction pressure poses an operational problem. In addition, the yield is low.
In the method of (2) above, the process spans a long period, and a large amount of waste effluent which contains harmful heavy metals can cause environmental pollution.
As stated above, both the known methods have various problems and are not industrially advantageous. For this reason, attempts have been made to develop an industrially advantageous method for production in the relevant technical field, but there is no satisfactory method.